1. Field of Invention
This invention relates to surveillance MAVs (micro air vehicles), specifically to those MAVs employing an insect-like topology to give the ability to fly very precisely and with great maneuverability and to perch, giving ability to scavenge energy from various sources, giving the ability to crawl terrestrially, and giving capability to deploy an offensive payload and return to point of origin.
2. Prior Art
Micro air vehicles (MAVs) are very useful tools for surveillance, incursion, and offensive payload deployment into areas where danger exists to personnel.
Current MAVs have a limited loiter time due to using circling or regularized flight at altitude to accomplish loiter. Previous approaches to extend MAV loiter have typically exploited very small, efficient fixed wing airframes that attempt to minimize the energy required to remain aloft. Because of this, the aircraft comprise a basic fixed wing plan form (wing, fuselage, rudder; wing, fuselage, rudder, stabilizer) and must remain at a range of at least loiter altitude from the target (hundreds to thousands of feet) while transmitting video and other surveillance back to the operator.
Disadvantages of these approaches are numerous and varied. First, accomplishing loiter by remaining aloft requires energy that could be used for some other purpose and constantly advertises the presence of the MAV to onlookers. Second, the shape of the common fixed wing aircraft plan form is easily recognizable, and because of this the MAVs purpose is easily surmised once spotted. Third, while increased loiter altitude lessens the delectability of the MAV it also decreases the quality of surveillance possible. Finally, because of the considerable wing span of most MAVs (when compared to fuselage length and other dimensions) and the significant forward velocity to remain aloft, motion into areas containing obstacles closer than together than several wing spans apart to get a closer view of the target is very problematic.
A MAV with a very compact, very maneuverable, and relatively unfamiliar plan form or topology that may perch on various objects would allow both the efficient translational flight and delicate maneuver required for perching and loitering, and eliminate the energy expenditure required to remain on station, while being able to conceal its presence while perched.
Current MAVs are very limited in the ability to perch and replenish of on board energy supplies, and thus have to return to their point of origin to extend mission duration, in the process losing contact with the target and doubling the exposure to unwanted observation. Prior attempts at MAV perching leverage the extreme thrust to weight ratio currently available to model aircraft fixed wing plan forms and require a ‘pitch up’ type of maneuver to transition the MAV from forward flight to a propeller based hover, finishing with the aircraft fuselage vertically oriented. Several modifications (including one very mathematical development) of the general fixed wing plan form have been attempted, including control of the stabilizer in similar fashion to a bird's tail during landing, but still require the transition of an aircraft from straight and level flight at high speed to hover with vertically oriented fuselage. The pitch up maneuver required to transition from efficient, high speed forward flight to hover for perching requires time and distance to accomplish, and thus runs increased risk of observation. Other perching attempts simply impact a power line or tree limb with a clamping mechanism which closes upon contact, with the aircraft momentum being dissipated in displacement of the wire or limb and in rotation of the aircraft about the wire or limb until forward kinetic energy is dissipated!
A MAV that may easily perch on a structure, without complex or risky maneuver, and remain motionless while gathering surveillance, without the immediately recognizable characteristics of fixed wing plan forms would greatly extend MAV missions as well as be much less detectable while perched.
Previous approaches to energy scavenging or energy harvesting have used lightweight, high power solar cells on the horizontal surfaces of the plan form (mainly wings and horizontal stabilizer) or a clamp around current transformer to inductively gather energy from an overhead wire.
While readily usable, solar power is relatively incapable of quick mission turnaround for recharging of propulsion batteries. Inductive scavenging of power lines has greater possibility for fairly rapid energy capture, but is relatively inefficient, bulky, heavy, and requires an almost prohibitively complex mechanism for clamping the current transformer onto the elevated wire and releasing it against a strong magnetic field (the current transformer must open wide and then close to an internal diameter very close to that of the wire being clamped for maximum energy transfer, all while in motion), making accurate perching problematic in unsettled or windy conditions or at even moderate forward velocities. Additionally, since magnetic field scavenging is completely dependent upon the current in the wire at any given time, an energized but unloaded distribution wire is useless as an energy source.
A MAV that may scavenge energy quickly and easily, with little maneuver or mechanical encumbrance and not dependent on the load attached to the power line circuit, would be able to deploy and loiter on station for exceptionally extended periods of time.
Current MAVs are virtually unable to crawl along the ground or relatively improved surface because of wingspan, bulkiness, unsuited propulsion, and turning difficulties. Previous approaches to MAV crawling are also very basic, including simple powered taxi on fixed, existing landing gear and complex folding wings to facilitate terrestrial maneuver in tight places.
The disadvantages of the prior approaches are the inability to overcome obstacles much larger than wheel diameter or landing gear length, the use of noisy and inefficient propeller thrust for terrestrial motion and subsequent waste of MAV energy, poor rough surface taxi characteristics of tricycle landing gear topologies, interferences with obstacles due to wing span, and the weight and complexity penalty incurred by employing wing folding mechanisms. All lessen MAV range, endurance, and payload carriage.
A MAV that could travel and navigate terrestrially without undue restriction would have the advantage of approaching targets or objectives to close proximity while the MAV was on the ground.
Finally, current MAVs are usually unarmed, or if armed cannot deploy an offensive payload without self destructing. Previous approaches to arming MAVs have been simply the carriage of explosive or ordinance that upon use resulted in the total loss of the MAV and with it the ability to ascertain damage to the engaged target. In addition to the immediate loss of surveillance capability, scattered MAV remnants may be used to identify its country of origin, its perch position, or ultimately the position of the operator.
A MAV that could carry a significant offensive payload, expel it, and return to the operator would be reusable and would lessen the possibility of exposure of the operator, the MAV country of origin, and the mission to the target or objective, while providing the ability to ascertain effect of payload deployment on the target.
U.S. Pat. No. 7,665,688 (Cylinder et al, 2010) claims a complex MAV that has multiple motors, flight surfaces, and flight modes. The MAV consists of a horizontal fuselage supporting a tilting, forward canard that in turn supports two motors and propellers, a center counter rotating pair of airfoil wings, and a nearly conventional rudder and fin layout at the rear of the fuselage. Because of this layout, the MAV may hover with the canard propellers tilted to vector thrust downward and a center motor spinning the center counter rotating airfoils, may perform forward flight in this configuration, and may lock the center counter rotating airfoils in place, rotate the canard supported propellers to horizontal, and fly akin to a conventional canard based, fixed wing design.
U.S. Pat. No. 7,665,688 differs considerably from the MAV contemplated herein. First, for necessity of balance its fuselage must remain horizontal or nearly so. Second, because of the weight and thrust layout, the rear tail surfaces begin to hint at the common fixed wing plan form and thus are recognizable. Third, the anti torque counter rotating mechanism employed swings two individual, complete airfoils (of large combined span) in opposite directions, with little evidence of counterbalance, flapping, advance or other mitigating techniques commonly used in full scale rotorcraft to combat thrust asymmetries. Fourth, crawling appears to be only possible with center counter rotating airfoils rotated longitudinally and the vehicle being pulled by front propeller thrust. Finally, it has no ability to perch on wires or tree limbs and dictate its direction of orientation while perched, no apparent scavenging capacity or apparatus, and no deployable payload is mentioned.
U.S. Pat. No. 7,658,346 (Goossen, 2010) claims a double ducted fan without central fuselage that uses moveable tail cones and speed brakes to effect control in pitch, roll, and yaw. The MAV in U.S. Pat. No. 7,658,346 is designed to carry payload as selected by soldiers, and mentions surveillance as an accompanying purpose. This disclosure also mentions the difficulties of center of gravity control for the side by side, double ducted design, a problem solved by the insect-like topology contemplated herein. Additionally, the MAV claimed in U.S. Pat. No. 7,658,346 cannot crawl, cannot perch on a wire, has no scavenging capability, and is depicted solely power by internal combustion motors, the carriage of fuel for which is not favored by US military operations.
U.S. Pat. No. 7,398,946 (Marshall, 2008) claims a fixed wing MAV carrying a magnetic induction, clamp on apparatus for ‘parking’ on a power line and extracting energy from the magnetic field surrounding the conductor. Much of the detail of the aerodynamic function of the MAV is left unexplained and unclaimed, with simultaneous propulsion and lift sources embedded in lifting wings, depicted in drawings but not sufficiently described. The MAV claimed in this patent includes surveillance sensors and transmitters of various types, includes carriage of an ‘weapon’ payload, and even claims a method of military of release, parking on a power line for energy replenishment, surveillance during the period of parking, and possible return to point of origin or redeployment and relocation.
The MAV claimed in U.S. Pat. No. 7,398,946 differs from the MAV contemplated herein in several significant areas. First, the MAV is depicted as having an easily recognized, fixed wing layout. Second, its method of energy scavenging from power lines is magnetic, meaning that it carries a complex, heavy, and bulky champing mechanism to concentrate the magnetic field around the power line. Most importantly, though, this type of energy scavenging is completely dependent on the amount of current flowing through the power line and cannot take advantage of the elevated electrical potential of the power line (indeed the elevated potential creates difficulties for the claimed MAV, as admitted by Marshall). If the current in the power line is small (as it will be designed to be, since as power line voltage potentials increase, current decreases to conserve I2R losses), induction energy available will decrease to possibly negligible levels. Also, this inductive clamp on approach cannot gather energy from high voltage DC transmission systems, present in the Middle East and elsewhere.
To accomplish perching, the MAV does not hover but simply flies at moderate speed forward until impact closes the clamping system. Provision is made for Hall effect sensing of the field around the ‘parking’ wire, but such sensing is extremely short range and of dubious utility for approach to the power line at distances greater than several inches. Additionally, it is assumed that once clamped the MAV may spin about the ‘parking’ wire until its forward kinetic energy is dissipated. No capacity for hover or very slow flight is claimed, and no capacity for electric field scavenging is claimed. No capacity for leveraging corona effects or a coronal virtual ground is claimed. U.S. Pat. No. 7,398,946 claims minor ability to orient the MAV while perched, but apparently in only two orthogonal directions, and in conjunction with ‘parking’ while flying parallel to the power line (again at appreciable forward velocity, claimed 35 MPH). The MAV claimed cannot crawl unless it lands and taxis on depicted landing gear, and the part of the military mission that would include landing on terra firma and crawling to get a close view of an objective, or crawling to engage personnel, vehicles, or structures on the ground, is not claimed or even mentioned.
U.S. Pat. No. 7,318,564 (Marshall, 2005) is authored by the same applicant as U.S. Pat. No. 7,398,946, contains virtually identical technology, and thus also differs from the MAV contemplated herein as previously described.
Various winged and flapping disclosures, specialty airfoils, launching pads, flying attachments to cell phones, wing combinations, wing articulations, hydrogen peroxide propulsion systems, chemical muscles, flapping entomopters (U.S. Pat. Nos. 7,651,051; 7,487,937; 7,658,347; 7,331,546; 7,252,265; 6,959,895; 6,938,853; 6,783,097; 6,766,638; 6,565,039; 6,446,909; 6,206,324 and 6,082,671) all claim aspects of insect flight that have utility, but none save U.S. Pat. No. 6,082,671 claim an entire MAV vehicle, and the remainder claim aspects unused in the MAV contemplated herein.
Additionally, various man sized dual ducted fan jet packs, such as the Martin Jet Pack, and multi rotor MAVs such as the DraganFly series have aspects of the MAV contemplated herein, but do not combine the insect-like flight features with the versatilities of perching, scavenging, crawling, and payload expulsion.
Spark gap based energy harvesting for scavenging is known in the literature and typically involves a direct connection to earth ground to function and keep involved circuitry from floating to unacceptably high potentials. In no cases, though, does the deliberate initiation of corona losses (which can be greater than tens of watts per meter of conductor) substitute for and function as the earth ground to sustain a high frequency relaxation oscillation for weight and size reductions beneficial for use with scavenging MAVs.
In short, the prior art does not contain a micro air vehicle with the requisite features to achieve insect like flight and thus achieve extreme mission versatility. All prior approaches are deficient in at least one of the following required features:                a. an insect-like topology to simultaneously provide very precise hover, efficient slow and fast flight, extreme maneuverability, small physical dimensions, ease of perching, and give appearance deception and camouflage capabilities;        b. highly integrated, simultaneous scavenging capability from solar, medium and high potential electric fields, and wind currents;        c. highly integrated ability to land and crawl terrestrially for surveillance advantage;        d. the ability to discharge an offensive payload in flying, perched, or crawling configurations to enable reuse and limit exposure of the presence and origin of operator and vehicle to discovery.        